Preliminary stage of a voltage regulator with low loss of voltag

Details Preliminary stage of a voltage regulator with low loss of voltag Preliminary stage of a voltage regulator with low loss of voltag

1989-08-16

1990-08-21

Beha, Jr., William H.

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

323276, 323277, 323279, G05F 1563

Patent

active

049509756

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a preliminary stage of a voltage regulator, and a voltage regulator with the preliminary stage.
Preliminary stages of voltage regulators and voltage regulators themselves, respectively, are already known, in which the charging current flowing in the capacitor, which serves as charge storage element on the output side, is reduced to zero when a series transistor reaches saturation. However, these arrangements have the disadvantage that the series transistor also carries a very high base current, which makes the regulator unsuitable for standby operation.


SUMMARY OF THE INVENTION

The object of the invention is a preliminary stage of a voltage regulator, which has the advantage that the increase in the base current of the series transistor is prevented during the reduction of the charging current of the capacitor in the event that the voltage difference between the input voltage and the output voltage falls below a predetermined amount, and which makes possible an efficient standby operation.
The object of the invention is achieved by providing a device which reduces the current flowing in the capacitor to zero before the series transistor reaches saturation when the input and output voltages fall below a predetermined magnitude.
The present invention both as to its construction so to its mode of operation, together with additional objects and advantages thereof, will be best understood from the following detailed description of preferred embodiments with reference to the appended drawings.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a known voltage regulator basic circuit;
FIG. 2 shows a known low-drop voltage regulator basic circuit;
FIG. 3 shows a known supplemental wiring of a low-drop regulator for a charge storage;
FIG. 4 shows a voltage regulator with a preliminary stage and subsequent regulator stages, according to the invention;
FIG. 5 shows an embodiment of a known low-drop preliminary stage of a voltage regulator;
FIG. 6 shows an embodiment of a low-drop preliminary stage of a voltage regulator, according to the invention;
FIG. 7 shows an embodiment of a subsequent voltage stabilizing regulator stage, according to the invention.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Voltage regulators for achieving the lowest possible voltage losses between the input and output voltage are known by a characterizing designations of "low-drop regulators" or "very-low-drop regulators" (e.g. L487, L387, etc. -SGS; TEA 7034-Thomson; LM2935-NS). They are used in motor vehicle electronic circuits, among other things, in order to ensure a sufficient 5V feeding of the vehicle electronic devices when the vehicle voltage drops to approximately 6V under starting load. Conventional drop voltages (minimum necessary voltage difference between input and output voltage) of such regulators lie between 0.6V and 1V.
Voltage regulators without low-drop characteristic (basic view in FIG. 1) work, in the regulator series arm or branch, with a power transistor T1 in voltage follower circuit (emitter follower) i.e., the emitter of the transistor T1 is at the output terminal 3 of the regulator on the load side and, accordingly, introduces no additional voltage amplification into the closed control loop (emitter T1; feedback divider R1, R2; inverting input of OP1; output of OP1 and base of T1). The internal frequency compensation of the operational amplifier OP1 controlling the final stage transistor, as described e.g. in US-PS 39 46 303, is sufficient for the stability of such regulators. The capacitor C1 parallel to the load terminals 2, 3 serves in this instance only as a charge storage for buffering the pulse loads which the regulator may not be able to level quickly enough. The regulator itself works in a stable manner also without the capacitor C1.
In contrast, the power transistor T2 lies in the series arm or branch of the voltage regulator of the low-drop type (basic view in FIG. 2) with its collector on the load side (terminal 3) and with its emitter on th

REFERENCES:
patent: 3048718 (1962-08-01), Starzec et al.
patent: 3373344 (1968-03-01), Seer
patent: 3946303 (1976-03-01), Streit et al.
patent: 4495536 (1985-01-01), Bynum
patent: 4684878 (1987-08-01), Giordano
patent: 4731574 (1988-03-01), Melbert et al.
Ciscato et al., "Supply Regulation in Automotive Electronics", New Electronics, vol. 18, No. 10, pp. 77, 8, May 14, 1985.
Thomson, Semiconductors, "Low Dropout Voltage Regulator (TEA 7034", (undated).
National Semiconductor, "LM2935 Low Dropout Voltage Dual Regulator", Mar. 1983.
SGS, "Very Low Drop Voltage Regulators (L387)", 1981.
SGS, "Very Low Drop SV Voltage Regulator", L487), 1982.

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